Scimitar antenna

Lore & Background

The scimitar antenna was invented in 1958 by Edwin M. and William P. Turner. A U.S. patent was applied for on October 31, 1958, and granted on December 26, 1961; the inventors assigned the patent to the U.S. government, as represented by the Secretary of the Air Force. The antenna's shape is essentially a flat metal plate in a semi-circular or semi-elliptical form, with a wide end at one side and a narrow point at the other.

In the Apollo Program, the Block II Apollo command and service module carried a pair of elliptical VHF scimitar antennas on the Service Module walls. The antenna's scimitar shape was not externally visible because it had to be covered by a shroud for aerodynamic purposes. It radiated and received signals in an approximately hemispherical pattern, so two antennas were necessary to provide full omnidirectional coverage. VHF communication was used for ship-to-ground communication in Earth orbit and ship-to-ship communication with the Apollo Lunar Module. The earlier Block I design carried the scimitar antennas inside two semicircular strakes attached near the base of the Command Module, intended to improve aerodynamic stability during reentry, but the strakes were found unnecessary and were deleted; the antennas were moved to the Service Module in Block II.

The first two Lunar Modules to fly, Apollo 5 and Apollo 9, also carried a pair of VHF scimitar antennas for transmitting Developmental Flight Instrumentation (DFI) telemetry data. One was on the front face, just inboard of the right-hand side cockpit window, and the other on the left side of the aft equipment bay. Since the Lunar Module never operated in Earth's atmosphere, no aerodynamic covering was necessary, and the scimitar shape was externally visible. After Apollo 9, the Lunar Module was considered operational, so the DFI and scimitar antennas were not present on subsequent flights.

Military aircraft, typically long-range bombers in the 1960s, sometimes used VHF jamming to disrupt the voice communications of interceptor aircraft. This jamming required broadband, omnidirectional antennas, such as the scimitar. Difficulties in developing the WCLG-3B design of antenna for the AN/ALA-15(V) voice jammer, by Dynalectron Corporation, led to both patented techniques in precision-forming PTFE as dielectric components and a notable lawsuit over the termination of the U.S. Government contract to supply them.

Reader's Guide

The scimitar antenna's significance lies in its specialized application for VHF communication in both space and military aviation. Its semi-circular or semi-elliptical flat-plate design provided a broadband, omnidirectional pattern suited for environments where aerodynamic constraints or space limitations were critical. On the Apollo spacecraft, it enabled ship-to-ground and ship-to-ship VHF communication during Earth orbit, complementing the unified S-band high-gain antenna used for lunar distances. The antenna's use on the Lunar Module for telemetry data on early flights (Apollo 5 and Apollo 9) highlights its role in developmental testing. In the military context, the scimitar was employed for VHF jamming on long-range bombers, such as the B-52, to disrupt interceptor communications. The development of the WCLG-3B variant for the AN/ALA-15(V) jammer involved patented techniques in precision-forming PTFE as dielectric components and led to a notable lawsuit over contract termination, reflecting the technical and contractual challenges of the era. The antenna's legacy is tied to its successful integration into the Apollo Program and its use in Cold War electronic warfare.

Did You Know?

• The antenna's shape was not externally visible on the Apollo command and service module because it was covered by a shroud for aerodynamic purposes.
• Military long-range bombers in the 1960s used scimitar antennas for VHF jamming to disrupt interceptor voice communications.